Fluid-Thermal Analysis Tab

Setting Item

Notes

Analysis Type

Steady-State Analysis

There is no time dependency.

Steady-state Analysis/ Thermal Transient Analysis

The steady-state analysis is performed with the fluid solver. Using the results, the thermal transient analysis is performed.

(only where no buoyancy is taken into account, the viscosity is not temperature-dependent, and material properties depending on ambient values are not used)

Transient Analysis

Transient states are analyzed.

Options

Notes

Laminar Flow/Turbulent Flow

Executes calculation assuming the flows are either laminar or turbulent.

Flow Type

Internal flow or external flow can be selected.

This option affects two settings.

・ Outer boundary conditions are automatically determined.

(The automatic determination can be deselected on the [Fluid tab (Fluid-Thermal tab)] of the outer boundary condition. Refer to [Outer Boundary Condition] for how to set outer boundary.)

Refer to [Boundary Condition of Fluid Analysis] of the Technical Notes for the details of outer boundary types.

・The fluid domain depends on whether internal flow or external flow is selected for the behavior of the automatically created fluid. (if [Automatic Fluid Creation] selected)

If [Internal Flow] is selected, a fluid domain is created inside the solid domain.

If [External Flow] is selected, a fluid domain is created outside the solid domain.

Select Take Buoyancy into Account (Natural Convection) to calculate the natural convection.

This option must be selected if there are no forced inflow or forced outflow.
Also, this option must be selected if the internal convection in the closed domain is taken into account.

If this option is not selected, the convection will not occur in the closed domain. (Only thermal conduction is taken into account for the heat transfer.)

if [Automatic Fluid Creation] is selected, a model of fluid can be automatically created. The model of fluid is automatically created based on whether the internal or external flow is selected.

Click the button . The [Automatic Fluid Domain Creation] dialog will appear. Fluid type, shape, and other parameters can be set.

Initial Value/Restart

If Use the last analysis results is selected,
the previous results which were not converged or aborted can be used as initial values.

If Use another analysis results (Results Import) is selected, an analysis model that was already analyzed or the results file is used as the initial values for the calculation.

The analysis model or the results file is specified on the [Results Import tab]

Click the[Detailed Setting for Restart] button to show the dialog box.

If Calculate quasi-steady state is selected, the analysis with finite timesteps is applied when restarting.
Effective for the case where steady state solution does not exist or the analysis does not converge due to the non-steady vibration.
An instantaneous state of the vibration is output.

If Hand over the time is selected, the time of the previous analysis results or another analysis results is handed over.

If the results of the previous analysis were up to 10 s for example, this option allows the analysis to continue without removing the results up to 10 s of the previous analysis.
(It corresponds to selecting [Continue from the last session] on the [Transient Analysis tab])
If the fluid analysis is transient analysis and [Hand over the time] is not selected, the results up to 10 s are removed and the analysis starts using the results at 10 s as an initial value.

If the analysis type of fluid solver is steady-state or if transient analysis is applied for the thermal or diffusion analysis, all the previous results are removed and the analysis starts at 0 s.

Different analysis conditions from the previous analysis can be applied as well.

The setting here automatically determines the settings of "Continue from the last session" on the [Transient Analysis tab] and "Import Type" on the [Results Import tab].

Radiation Setting

Enables the settings relating to the radiation.

・Outer boundary condition setting

・Default value of emissivity

・Emissivity of each body attribute

・Emissivity of each boundary condition

Click to show [Radiation Setting] dialog box.

Diffusion Analysis

For diffusion analysis, select [Diffusion Analysis] in the [Option].

See Diffusion Analysis of technical note for more information.

Click to show the [Diffusion Analysis Setting] dialog box.

Free Surface Analysis (VOF Method)

For free surface analysis (VOF method), select [Free Surface Analysis (VOF method )] in the [Option].

See [Free Surface Analysis (VOF method)] for more information.

Click to show the [Multiphase Flow Setting]] dialog box.

Layer Mesh Setting

Enables the general settings for the layer mesh of the wall surface.
If the individual setting is not applied to each boundary condition, the settings here are applied.

Click this button . The Layer Mesh Setting dialog box will appear.

Ambient Value Setting

Refer to the [Ambient Value Setting] tab for more information.

In the fluid thermal analysis, set the ambient temperature on the [Ambient Value Setting] tab.

The ambient temperature is used in the following ways.

・Reference temperature for buoyancy

The buoyancy is calculated using the temperature difference from the ambient temperature.

・Inflow temperature, wall face temperature, and ambient temperature for boundary condition on the [Fluid tab (Fluid-Thermal tab)].

・Ambient temperature and ambient radiation temperature on the [Thermal tab].

・Unless specified individually, the ambient temperature set here is used as the ambient radiation temperature.

・Initial temperature for a transient analysis

・[Heat flux] on the result field

Heat flux is the sum of the heat flux by thermal conduction and the heat flux by advection.

The heat flux by the advection is calculated as "flow velocity" x "density" x "enthalpy".
Ambient temperature is used as a reference temperature for the enthalpy.

・[Coefficient of heat transfer for convection] on the result field.

It is calculated as "heat flux on wall face"/("wall face temperature" - "ambient temperature").

・Advection components of the heat balance and the heat flow rate.

The heat flow rate by the advection is calculated as "flow velocity" x "density" x "enthalpy".

Ambient temperature is used as a reference temperature for the enthalpy.

Click to show [Ambient Value Setting] dialog box.

Setup Details

Parameters relating to the accuracy and convergence are set.

Click to show [Detailed Setting of Fluid Analysis] dialog box.

Coupling State

Shows if the coupling is unidirectional or bidirectional.

If the temperature dependency of density (buoyancy) and of viscosity, non-Newtonian fluid, and material properties depending on ambient values are taken into account, the analysis is bidirectional (thermal to fluid and fluid to thermal).
The calculation load is increased as the number of iterations in the thermal analysis increases.

<One directional coupling: fluid ⇒ thermal>

The fluid analysis is performed first, then the thermal analysis is performed.

<Bi-directional coupling: fluid ⇔ thermal>

The fluid analysis and the thermal analysis are performed alternately.